Dealing with Oauth 2.0-facebook gem error 100: This authorization code has been used

Question

I have been working on setting up facebook authentication for my rails app and while testing, after logging-in with my facebook account, I keep getting this error:

Answer 1

I had this issue as well. I was seeing the "(facebook) Callback phase initiated." message twice in my Rails logs. It turns out that I was initializing FB authentication twice (I am using Devise and Omniauth-Facebook), and I'm guessing one of these was attempting to reset the access token.

Disabling the initializer in Omniauth-Facebook (config/initializers/omniauth.rb) fixed my issue.